MX2012014671A

MX2012014671A - Hybrid arc/laser-welding method for aluminized steel part using a gas including nitrogen and/or oxygen.

Info

Publication number: MX2012014671A
Application number: MX2012014671A
Authority: MX
Inventors: Francis Briand; Olivier Dubet
Original assignee: Air Liquide
Priority date: 2010-07-13
Filing date: 2011-05-05
Publication date: 2013-02-11
Also published as: CA2800246C; CN102985216A; US20130105446A1; JP6067555B2; RU2013105805A; CN102985216B; ES2554494T3; KR20130124471A; EP2593267B1; FR2962674B1; BR112013000894A2; RU2590759C2; CA2800246A1; EP2593267A1; FR2962674A1; JP2013532070A; WO2012007663A1; ZA201209342B

Abstract

The invention relates to a hybrid laser/arc-welding method using an electric arc and a laser beam that are combined together within a single welding bath, to which molten metal is supplied by melting a filler wire, wherein the welding bath is provided on at least one steel part including an aluminum surface coating, and a protective gas is used, characterized in that the protective gas consists of at least one main compound selected from argon and helium, and of at least one additional compound selected from nitrogen and oxygen.

Description

HYBRID METHOD OF SOLDEO WITH ELECTRIC / LASER BOWL FOR PARTS OF ALUMINIZED STEEL, USING A GAS THAT INCLUDES NITROGEN AND / OR OXYGEN The invention relates to a process for the hybrid welding with laser / electric arc, of steel parts comprising a surface coating based on aluminum, in particular a coating of aluminum and silicon, using a protective gas formed of argon and / or helium to which small proportions of nitrogen or oxygen are added.

Certain steels, called aluminized steels because they are coated with aluminum or with an aluminum-based alloy, such as USIBORMR steels, have very high mechanical characteristics after hot drawing and, therefore, are used more and more in the field of the construction of motor vehicles, when you wto reduce the weight. ' Certainly, these steels are designed to be thermally treated and then hardened during the hot drawing operation, and the mechanical characteristics that result allow a very significlightening of the vehicle's weight compared to a standard steel of high tensile strength. . They are mainly used to manufacture stop beams, reinforcements for doors, central uprights, window sills, etc. - - EP-A-1878531 proposes to weld aluminized steels of this type by the use of a hybrid welding process with laser / electric arc. The principle of hybrid welding with laser / electric arc is well known in the prior art.

However, in practice it has been observed that after an operation for hybrid welding, with a protective atmosphere formed of a He / Ar mixture, of the steel parts coated with aluminum or with an aluminum alloy, in particular a Al / Si type alloy and post-solder heat treatment comprising hot drawing at 920 ° C, then tempering at the tool (30 ° C / s), with a phase often showing lower tensile strength than the base metal and that the area of the weld metal in the welded joint.

However, this phase with a lower tensile strength constitutes a fragile area of the weld obtained thereby, as explained below. These more fragile zones appear within the martensite zone in the form of white phase islands containing aluminum aggregates originating from the surface layer.

After the analysis, it was determined that this phase contains an importpercentage of aluminum (> 2%) that gives rise to a non-austenitic transformation of the steel during the thermal treatment of the same before the stretching, that is to say - - that this phase remains in the form of delta ferrite and the result of this is a lower hardness than the rest of the part that has undergone a martensitic / bainitic transformation.

However, the phase not transformed into the martensite phase can result, during the mechanical characterization of the joint after welding and stretching followed by heat treatment, cracks or even a rupture by the shear stress of the welded joint, and that these areas that have aluminum incorporated, have a lower resistance than the welding. the metal deposited.

The problem that faces is therefore to propose a laser / electric arc hybrid welding process that improves the mechanical properties of the welded joint, during an operation to weld steel parts coated with a layer comprising aluminum. More specifically, the problem is to be able to obtain a homogeneous martensite-type microstructure in the area of the weld metal, ie in the weld joint, after hot drawing, typically at approximately 920 ° C and anneal in the tool. Stretched, typically with a cooling rate of between 800 ° C and 500 ° C of the order of 30 ° C / s.

The solution of the invention is a welding process - - hybrid laser / electric arc that uses an electric arc and a beam of lasers that combine with each other, particularly in a single weld pool, where the weld metal is provided by melting a consumable wire and the bath Welding melt is produced in at least one part of steel comprising a surface coating based on aluminum and wherein also use is made of a protective gas, characterized in that the protective gas consists of at least one main compound selected from argon and helium and at least one additional compound selected from nitrogen and oxygen.

According to the invention, the weld pool and therefore subsequently the weld joint are thus obtained in the joint plane formed by contacting, particularly end to end, the parts to be welded, by melting the steel constituent of the parts under the simultaneous action of a beam of lasers and an electric arc that combine with each other to melt the metal of the part or parts to be welded, while obtaining an additional provision of welding metal, also by virtue of of the consumable wire that is also melted, preferably by means of the electric arc, the weld metal thus obtained is deposited in the weld pool formed on the part or parts to be assembled.

According to the invention, in order to solve the - - The aforesaid problem is used as a protective atmosphere of the welding zone, in particular of the weld fusion bath, of a gas mixture that is formed only, on the one hand of argon, helium or both as compound (s) main (s) of the gas mixture and, on the other hand, of nitrogen or oxygen or even of the two as additional compound (s), in order to constitute a binary mixture of gas type Ar / N2, Ar / 02 , He / 02 or He / N2 or a ternary mixture of gas type Ar / He / N2 or Ar / He / 02 or even a quaternary mixture of gas type Ar / He / 02 / N2. In all cases, the proportion of the main compound (ie Ar or He) or the sum of the proportions of the main compounds (ie Ar and He) is greater than the proportion of the additional compound (ie N2 or 02) or the sum of the the proportions of the additional compounds (ie N2 and 02) present in the gas mixture.

Among these various gas mixtures that can be used, two gas mixtures are particularly preferred, since they lead to very good results, as explained below, ie the mixtures of Ar / N2 or Ar / He / N2 which contain at most 10% nitrogen (% by volume) and conveniently from 3% to 7% approximately nitrogen. In general, it should be noted that within the context of the present invention, unless otherwise indicated, all percentages (%) given are percentages by volume (¾ by volume).

- - Certainly, the implementation of a hybrid arc / laser welding process using a protective gas mixture formed of argon and / or helium, on the one hand, and nitrogen and / or oxygen on the other, makes it possible to obtain during the assembly of the aluminized steel parts, a welding joint of free or virtually free martensitic microstructure, of whitish ferrite islands, since the addition of 02 or N2 makes it possible to trap the aluminum that originates from the surface layer and that it releases during the fusion of said layer under the effect of the electric arc and the laser beam.

The entrapment of aluminum by the compounds of 02 or N2 leads to the formation of compounds type A1203 or A1N, thus avoiding the formation of ferrite or other harmful intermetallic compounds. In fact, the aluminum oxides or nitrides thus formed float on the surface of the bath, thereby preventing the dissolution of the aluminum in the weld pool.

The result of this is the suppression or at least the considerable reduction of the incorporation of the aluminum in the weld, therefore it is commonly observed An improvement of the tensile strength due to the total or virtually total disappearance of the whitish phase of ferrite delta.

Depending on the case, the process of the invention may comprise one or more of the following characteristics: - - The protective gas contains from 1% to 20% by volume of said at least one additional compound. the protective gas contains from 1% to 15% by volume of said at least one additional compound. - the protective gas contains at least 2% by volume of said at least one additional compound. the protective gas contains at most 10% by volume of said at least one additional compound. the protective gas contains only nitrogen, as an additional compound. the protective gas contains at least 4% by volume of nitrogen, as an additional compound. the protective gas contains at least 5% by volume of nitrogen, as an additional compound. - the protective gas contains at most 8 by volume of nitrogen, as an additional compound. the protective gas contains at most 7% by volume of nitrogen, as an additional compound. the protective gas contains at least 5.5% by volume of nitrogen and at most 6.5% by volume of nitrogen. the protective gas is a mixture of He / Ar / N2- P Ar / N2. the steel part or parts comprise an aluminum-based surface coating having a thickness between 5 and 100 μm, preferably less than or equal to 50 μm. The coating covers at least one surface of the part or - - parts, but preferably no or virtually no aluminum coating is present at the edges of the ends of said part or parts, i.e. for example, at the edges of a sheet. the metal part or parts are produced from steel with a surface coating based on aluminum and silicon, preferably the surface coating contains more than 70% by weight of aluminum.

The metal part or parts are produced from steel with a surface coating consisting essentially of aluminum and silicon (Al / Si). the metal part or parts comprise a surface coating based on aluminum and silicon containing an aluminum content between 5 and 100 times greater than that of silicon, for example a proportion of aluminum of 90% by weight and a proportion of silicon of 10% by weight, ie a surface coating layer comprising 9 times more aluminum than silicon. the metal part or parts comprise a surface coating based on aluminum and silicon containing an aluminum content between 5 and 50 times that of silicon, especially an aluminum content between 5 and 30 times greater than that of silicon, in in particular, an aluminum content between 5 and 20 times that of silicon. _ _ several parts are welded together, typically two parts; it being possible for said parts to be identical or different, in particular in terms of shape, thickness, etc. the parts are produced from highly alloyed steel (> 5% by weight of alloying elements), weakly alloyed steel (<5% by weight of alloying elements) or non-alloy steel, for example a carbon steel.

The welding wire is a solid wire or a wire with a flux core. - the welding wire has a diameter between 0.5 and 5 mm, typically between approximately 0.8 and 2.5 ram. the consumable wire is fused by the electric arc, preferably an electric arc obtained by means of a welding torch MIG. - the consumable wire contains carbon and / or manganese (min 0.1% C and min 2% Mn).

The part or parts to be welded are selected from designed preforms and pipes. > the part or parts to be welded are components of exhaust silencers. the parts are placed and welded in an I-shaped weld configuration.

The electric arc is generated by a welding torch of the MIG type (Metal Inert Gas). - the laser beam is generated by a laser generator - - or C02 / YAG device, fiber, especially ytterbium or erbium fiber or disk type. the laser beam precedes the MIG arc during welding, when considering the direction of the solid.

The MIG welding regime is of the short air type. the welding voltage is less than 20V, typically between 11 and 16V.

The welding intensity is less than 200 A, typically between 118 and 166 A. - the speed of the welding is less than 20 m / min, typically between 4 and 6 m / min. the part or parts to be welded have a thickness between 0.8 and 2.5 mm, preferably between 1.8 and 2.3 mm. The thickness is considered to be produced in the plane of union, that is to say at the place where the metal is melted in order to form the welding joint, for example at the terminal edge of the part or parts to be welded.

The solder joint has a martensitic structure. - the gas pressure is between 2 and 15 bar, for example of the order of 4 bar. the gas flow rate is between 10 and 40 1 / min, typically of the order of 25 1 / min. the focal point of the laser beam is focused above the part to be welded and in a range of between 3 to 6 mm. the distance between the filler metal wire and the laser beam must be between 2 and 3 mm. various parts are welded together, typically two parts. - the gas mixture used in the context of the present invention can be produced either directly at the site by mixing the constituents of the mixture in the desired proportions using a gas mixer or being in pre-packaged form, ie produced in a packing factory and subsequently transported to its place of use in suitable gas containers, such as gas cylinders for welding.

The invention will be better understood now, because of the following description and examples made to show the effectiveness of the electric arc / laser hybrid welding process of the invention.

Examples The laser / electric arc hybrid welding process according to the invention gave good results during the implementation thereof for hybrid welding, using a C02 type laser source and a MIG arc welding torch, of coated steel parts with a layer of approximately 30 μp? of an aluminum / silicon alloy in respective proportions of: 90% and 10% by weight.

The welded parts have a thickness of 2.3 mm.

Within the context of the tests carried out, the gas used, which is supplied at a flow rate of 25 1 / min and at a pressure of 4 bars, is: - Test A (comparative): ARCAL 37 mixture formed of 70% helium and 30% argon, Test B: ARCAL 37 mixture to which 6% of N2 is added. Test C: ARCAL 37 mixture to which 3% of 02 is added.

The ARCAL 37 mixture is sold by Air Liquide. The torch used is an OTC reference MIG torch powered by a Nic 535 (0.7% C and 2% Mn) type filler metal wire having a diameter of 1.2 mm, which is supplied at a rate of 3 m / min. .

The welding voltage is about 15 V, and the intensity is about 139 A, which is obtained by virtue of a generator type Digi @ wave 500 (short arc / short arc +) in synergistic mode (EN 131) marketed by Air Liquide Welding, France.

The laser source is a C02 laser oscillator that has a power of 12 k.

The welding speed achieved is 4 m / min.

The parts to be welded are preforms designed for welding in I produced aluminized steel (Al / Si) type Usibor 1500MR.; - - The results obtained show that the presence of N2 in the argon / helium mixture leads to much better results than the tests without nitrogen in the protective gas.

Similarly, the presence of a small proportion of 02 in a mixture of argon / helium makes it possible to counteract the effect of suppressing the austenitic transformation caused by the presence of aluminum in the area of the weld metal.

Certainly, when using the mixtures of Ar and / or He and N2 and / or 02 according to the invention, a significant improvement in the results is therefore observed, the improvement of which increases proportionally to the content of N2 or 02 in mix. In fact, the micrographs 1 show that, in both cases, the white phases have disappeared completely, whereas this is not the case with the ARCAL 37 mixture alone.

In addition, with the additions of 02 or Ñ2, the resistance to rupture of the union, after the. Austenitization and tempering, is equivalent to that of the base metal.

The results obtained during the tests show that an addition of nitrogen to argon and / or helium makes it possible to significantly improve the welding quality of steels coated with a surface layer of aluminum / silicon alloy, in particular a homogeneous martensite-type microstructure in the Welding metal zone.

The improvement is even more significant when the - - Nitrogen content is increased but with an optimum of less than 10% by volume, which would induce the use of approximately 6% to 7% nitrogen in argon or in argon / helium.

The improvement is even more significant when the oxygen content is increased, but with an optimum of less than 10% by volume, which would induce the use of approximately 3% to 5% nitrogen in argon or in argon / helium.

The process of the invention is particularly suitable for the welding of designed preforms used in the field of the construction of motor vehicles of components of exhaust silencers, in particular for vehicles and for the welding of pipes.

Claims

1. A hybrid welding process with laser / electric arc using an electric arc and a beam of lasers that are combined together, producing a weld fusion bath on at least a part of steel comprising an aluminum-based surface coating , wherein the welding metal is provided by melting a consumable wire and wherein a protective gas is also used, characterized in that the protective gas consists of at least one main compound selected from argon and helium and from at least one compound additional selected nitrogen and oxygen.

2. The process as claimed in claim 1, characterized in that the protective gas contains from 1% to 20% by volume of said at least one additional compound.

3. The process as claimed in one of the preceding claims, characterized; wherein the protective gas contains from 2% to 10% by volume of said at least one additional compound.

4. The process as claimed in one of the preceding claims, characterized in that the protective gas contains only nitrogen as an additional compound.

5. The process as claimed in one of the preceding claims, characterized in that the protective gas contains from 4% to 7% by volume of nitrogen as an additional compound.

6. The process as claimed in one of the preceding claims, characterized in that the protective gas is a mixture of He / Ar / N2 or Ar / N2.

7. The process as claimed in one of the preceding claims, characterized in that the steel part or parts comprise a surface coating based on aluminum having a thickness between 5 and 100 μt, preferably less than or equal to 50 μm.

8. The process as claimed in one of the preceding claims, characterized in that the metal part or parts are produced from steel with a surface coating based on aluminum and silicon, preferably, the surface coating contains more than 70% by weight of aluminum .

9. The process as claimed in one of the preceding claims, characterized in that the consumable wire is melted by the electric arc, preferably an arc obtained by means of a welding torch MIG.

10. The process as claimed in one of the preceding claims, characterized in that the consumable wire contains carbon and / or manganese (min 0.1% C and min 2% Mn).

11. The process as claimed in one of the preceding claims, characterized in that the part or parts to be welded are selected from designed preforms, pipes or components of exhaust silencers.

12. The process as claimed in one of the preceding claims, characterized in that the parts are placed and welded in a weld configuration in I.